A wind turbine tower is generally 30-80 m in height and has a diameter of 2-10 m. Typical modern tower weights are 40 tons for a 50 m tower for a turbine with a 44 m rotor diameter (600 kW), and 80 tons for a 60 m tower for a 72 m rotor diameter. Due to the height and weight of the wind turbine tower, the forces formed by rotational movements of the wind turbine blades, and the very large surface of the tower being exposed to the wind, the tower must be steadily fastened to the ground.
Depending on soil conditions, for example rock, soil or gravel, different kinds of foundations are used for securing the wind turbine tower to the ground. One way of forming a foundation is to form a concrete foundation in a recess, arrange a support structure on the concrete foundation, form a connection to the tower, and arrange anchors into drilled holes in the ground for securing the foundation to the ground.
Another type of foundation for a wind turbine is a mono pile foundation. The mono pile foundation comprises a tubular element, having a length exceeding the diameter, which is forced into the ground by hammering or vibrating. This technique works well as long as the ground does not contain any unexpected objects, like rocks. However, the mono pile is subjected to very large forces when being hammered into the ground. Consequently, the mono pile must be reinforced in order to resist the forces resulting from the hammering. Additionally, vibrating the mono pile into the ground works well in sand but not in clay.
WO 01/66861 discloses a device and a method for anchoring a foundation for a wind turbine tower to a rock bed. This solution represents an embedment foundation, as the anchoring portion is embedded in concrete and may be provided with anchors, and the height of the anchoring portion approximately corresponds to the diameter of the anchoring portion.